I. Field of the Invention
The present invention relates generally to apparatuses for the drilling of oil and gas wells from barges or other vessels, and more particularly to drilling substructures which can be moved to drill two or more wells without relocation of the barge.
II. Description of Prior Art
In the oil and gas industry, the terrain above the suspected location of hydrocarbon products is largely determinative of the type of machinery used to drill the necessary wells. Onshore drilling operations generally require the least amount of preparation and expense, whereas as deep offshore locations typically require massive underwater frames to support the drilling operations above the water. In most cases, the drilling platform is relatively stationary. However, there are many instances, such as in lakes, swamps and other shallow water areas, in which the terrain allows for the use of barge drilling vessels. The two major classes of drilling barges are bay (or swamp) barges and posted barges. Both types of drilling barges are self-contained drilling systems which can be floated to a desired location by a tugboat or similar means and caused to be stabilized with respect to the ground. In the case of posted barges, three or more vertical posts are jacked downwardly into the mud below the surface of the water until the entire barge and its associated drilling platform are stabilized. In the case of bay barges, the ballasting system of the barge is manipulated until the bottom of the barge rests firmly on the bottom of the river or bay. In either type of drilling barge, once the barge is properly stabilized, the derrick is hingeably raised to its operating position, and the well can then be drilled through a keyway formed into the drilling barge below the drilling platform. After the well is drilled, the barge is moved away from the site so that other activities related to production and completion of the well can be conducted. In this manner, the barge can be moved relatively easily from one drilling site to the next by simply floating it to another location. However, there are distinct disadvantages to the requirement of moving the barge in order to drill another well.
Moving the barge requires complete cessation of drilling activities, lowering the derrick, and conducting numerous preparatory tasks prior to moving the vessel. Of course, the entire drilling system must again be placed into its operational configuration once the barge is relocated, consuming even greater time and expense prior to the actual drilling process. In addition to concerns over time and expense, relocation of the barge is sometimes impossible or ill advised, depending upon the underlying terrain or numerous other factors. A particularly poignant example of a situation in which relocation of the barge would be undesirable is in drilling operations in certain parts of Nigeria. Many of the drilling sites in that country are along small rivers and streams having exceedingly soft bottoms. The narrow spaces within which the barge must operate make it difficult to reposition the barge for each well to be drilled. Also, the soft river bottoms require more careful and time-consuming ballasting and deballasting of the vessel than in other environments to ensure a stable platform for the drilling operations. Relocation of the barge under these conditions, therefore, is at best an expensive undertaking, and at worst an impossible task.
Finally, the need for frequent relocation of the barge makes it difficult to maintain an adequate security perimeter around the barge. In Nigeria, as well as in other third world countries experiencing political unrest, such drilling operations are a frequent target of vandalism and terrorism. Consequently, it is often necessary to construct fences or barricades around the barge to prevent unauthorized access to the drilling equipment and personnel. Such security measures must often be dismantled and reconstructed during the relocation of the barge, thereby jeopardizing valuable equipment and crew members during these windows of vulnerability.
Based upon the aforementioned problems associated with relocation of the barge, there is a distinct need in the industry for a barge drilling system which would permit the drilling of two or more wells while the barge remains stabilized at a single location. In such a proposed system, the barge would remain in a particular location, while the drilling substructure is moved relative to the barge to drill one or more wells in a pattern. Ideally, after a first well is drilled, production and completion operations can be conducted on the first well, simultaneous with the drilling of a second or subsequent well adjacent to the first drilled well. The movable substructure would include a hoisting system suspended from underneath the drill floor, as well as a skate system at the base of the substructure, for easily moving heavy equipment, such as blow out preventers (BOP's) to and from the wells that have been drilled. Because the barge would remain situated during the maintenance of previously drilled wells, a protective deck would also be employed above the well protect structure for use by crews around those wells undergoing production.